1. Field of the Invention
The invention relates to an image forming apparatus and, more particularly, to the hue correction of an image forming apparatus having a full color two-sided printing function.
2. Related Background Art
In recent years, a digital color copying apparatus in which a color image reading apparatus using a CCD or the like and a color image recording apparatus of a laser beam printer (hereinafter, referred to as an LBP), an ink jet printer (hereinafter, referred to as an IJP), or the like are combined has been developed, so that a multicolor original can be read and recorded with a high fidelity including a color tone or the like.
There is, consequently, the demand for such a digital color copying apparatus is increasing every year. A demand to provide various intelligent functions for the digital color copying apparatus is also increasing greatly. One of such functions is a full color two-sided printing function.
The above conventional apparatus, however, has the following problems.
In a color copying apparatus of the electrophotographic type, an electrostatic latent image formed on a photo sensitive drum is developed to a toner image by a developing apparatus and the toner image is copy transferred onto a recording paper by a copy transfer apparatus. After that, the toner image is fixed onto a recording paper by a fixing apparatus. In this case, the fixing apparatus fixes the toner image by twining the crushed particle-like toner and the fibers of the recording paper by using heat energy and pressure.
There is consequently a tendency such that the hue of the color of the lowest layer of the surface (hereinafter, referred to as an A side) of the recording paper onto which an image is first printed is enhanced because the toner is twined to the fibers of the recording paper. In the two-sided recording mode, since fixing energy is applied to the A side even during the fixing operation of the surface (hereinafter, referred to as a B side) of the recording paper onto which the image is printed at the second time, the toner of the color of the lowest layer of the A side is more densely twined with the fibers of the recording paper, so that the hue is further enhanced. On the other hand, upon fixing of the B side onto which the image is printed at the second time, since the fibers of the recording paper have already been crushed when the A side is printed, it becomes difficult to twine the toner of the B side and the fibers of the recording paper and a density of the whole image formed decreases.
As a result, the conventional apparatus has a drawback such that when the two-sided printing operation is executed, the hue of the image printed on the A side is different from the hue of the image printed on the B side.
Similarly, the conventional apparatus has a drawback such that the hue in the case where the same image is printed in the one-side printing mode is different from the hue in the case where the same image is printed in the two-sided printing mode.
For example, in the conventional apparatus, in the case of sequentially recording in accordance with the order of magenta M, cyan C, yellow Y, and black K, upon fixing of the B side, the M toner on the A side is subjected to a fixing energy that is larger than those of the other three colors and the M toner is densely twined with the fibers of the recording paper and a color image is derived. As a result of it, the conventional apparatus has a drawback such that a whole image, printed on the A side is set to a magenta-like color and an image quality is lost.
Such drawbacks occur not only by the fixing as mentioned above but also by a difference between the image forming states between the A side and the B side, a difference of the copy transferring efficiency between the A side and the B side in a color printing apparatus of the electrophotographic type, or the like.
In the above color printing apparatus, the fixing state is different where the recording material is thick from that where the recording material is thin, so that there occurs a problem such that the coloring states of the coloring agents which are developed are different and the hue changes.
Such problems therefore occur not only in the two-sided recording apparatus but also in the case of using recording materials of different thicknesses.